Stock Exhaust Header Mod (Open Up)

[hornetgod13]

I took a tip from TRXRacer1 and decided to open up the stock header. I took a few before and after pictures and measurements. The stock header collar welds are excessive and restrictive. With a little coaching and guidance from TRXRacer1, I used an assortment of dremel tool attachments to grind down and polish the welds to match the inside diameter of the header. The results were amazing! The before and after measurements showed an 11.2% (1/8") increase in each header pipes diameter. I'm not a rocket scientist but, I'm smart enough to know that an increase of airflow on a 4 stroke engine leads to more power.

This is an easy mod to do that took less than an hour to do from start to finish. It would go perfectly with a slip-on exhaust to maximize the benefit.

Here's some pictures...

[hornetgod13]

Here's a picture of one stock welded header pipe and the other after I opened it up another 1/8th of an inch.

[hornetgod13]

Here's a picture of the caliper I used to measure the difference. The before and after measurements on each pipe was .125 of an inch which converts over to 1/8 of an inch. That was an increase of 11.2% over the stock header welds.

i've been wanting to do this for awhile but i wasnt sure of what to do thanks for the thread the pictures explain so much. What did you do with all the shaving that went everywhere from grinding it down? dont they go into the headers?

[hornetgod13]

Originally posted by FoxHondaRider
What did you do with all the shaving that went everywhere from grinding it down? dont they go into the headers?

I blew the metal grindings out with an air hose and once it was installed the motor blew out anything that was left over.

[STUNTIN400EX]

GREAT POST! I WILL HAVE TO DO THIS ONCE MY HMF SLIP ON GETS HERE! BY THE WAY YOU HAVE AN AWESOME QUAD.

[flauge]

Did you notice a good gain? Im probably gonna do this when i get my hmf. Also did you reuse the exhaust gaskets?

[hornetgod13]

Originally posted by flauge
Did you notice a good gain? Im probably gonna do this when i get my hmf. Also did you reuse the exhaust gaskets?

Since they are crush gaskets, I would suggest you use new ones to ensure no exhaust leaks. I installed new gaskets.

When the weather improves I'll take it out and test it however, I've done so much to my quad since they last time I rode it that it will be impossible to pin point how much this mod actually did to help the performance.

[maxfior]

Nice work hornetgod13! I've been planning on doing the exact same thing but I'm waiting on my dad's die-grinder. Nice pictures and good work with the micrometer, that's a great way to show how much material could be removed!

Max

[trx400EXtreme]

it's as simple as that? that grind doen the welds?

[hornetgod13]

Originally posted by trx400EXtreme
it's as simple as that? that grind doen the welds?

Yes, it's just that simple.

[XXXRACER165]

Originally posted by hornetgod13
Since they are crush gaskets, I would suggest you use new ones to ensure no exhaust leaks. I installed new gaskets.

When the weather improves I'll take it out and test it however, I've done so much to my quad since they last time I rode it that it will be impossible to pin point how much this mod actually did to help the performance.


I agree with only using new exhaust gaskets. This is a great modification for engines 426cc's & under but I have also done this and tested it on my 440 and the main round tube at the end (outlet) just isn't big enough for best top-end power. It doesn't flow enough air. Plus, I have also tested the scavenging of the stock header compared to my White Brothers "Works" head pipe and the stock header doesn't scavenge very well. The left side (the part in the picture you didn't polish yet), that tube is too long. WB reworked the header so when a pulse goes through one port, it sucks even more exhaust through the other port. Thus completely scavenging all the exhaust out of the cylinder. I hope I explained it right. :ermm:

[zrpilot]

Originally posted by XXXRACER165
I agree with only using new exhaust gaskets. This is a great modification for engines 426cc's & under but I have also done this and tested it on my 440 and the main round tube at the end (outlet) just isn't big enough for best top-end power. It doesn't flow enough air. Plus, I have also tested the scavenging of the stock header compared to my White Brothers "Works" head pipe and the stock header doesn't scavenge very well. The left side (the part in the picture you didn't polish yet), that tube is too long. WB reworked the header so when a pulse goes through one port, it sucks even more exhaust through the other port. Thus completely scavenging all the exhaust out of the cylinder. I hope I explained it right. :ermm:

I have seen this phenomenon as well and it creates a lean spike due to the unequal runner lengths. There are very FEW 2-into-1 headers that solve this problem. Laz made some once and has threatened to make more. The Sparks and WB exhausts are pretty good. The DMC Alien (dual header) does NOT have this issue!

If you look at the dynojet graph for their jet kit, you will see this.

NICE POST!

[Hondamaster5505]

Originally posted by zrpilot
I have seen this phenomenon as well and it creates a lean spike due to the unequal runner lengths. There are very FEW 2-into-1 headers that solve this problem. Laz made some once and has threatened to make more. The Sparks and WB exhausts are pretty good. The DMC Alien (dual header) does NOT have this issue!

If you look at the dynojet graph for their jet kit, you will see this.

NICE POST!

I have the DMC!

sorry, i couldnt help myself.:p

so your saying that the 2 headers running straight back is a better system and a 2-1?

(btw hornetgod, im not trying to hijack your thread, sorry.)

[hornetgod13]

Originally posted by XXXRACER165
I agree with only using new exhaust gaskets. This is a great modification for engines 426cc's & under

Thanks for the advice. I will keep it this way. I was on the fence on wheather of buy a new full exhaust or mod the stock header and keep the HMF slip-on installed.

[TRXRacer1]

Good work hornetgod13! It's surprising how much is to be gained there. That's about how mine looked when I did this mod. Good job on the write up.

[zrpilot]

Originally posted by Hondamaster5505
I have the DMC!

sorry, i couldnt help myself.:p

so your saying that the 2 headers running straight back is a better system and a 2-1?

(btw hornetgod, im not trying to hijack your thread, sorry.)

As XXXRACER165 and I have stated, the unequal length headers that most exhaust companies build for the 400EX have an unusual effect that leads to this lean condition.

The DMC uses longer head pipes and the exhaust pulses are not strong enough when they meet in the silencer to effect one another.

[Hondamaster5505]

Originally posted by zrpilot
As XXXRACER165 and I have stated, the unequal length headers that most exhaust companies build for the 400EX have an unusual effect that leads to this lean condition.

The DMC uses longer head pipes and the exhaust pulses are not strong enough when they meet in the silencer to effect one another.

so is that why its running alright without being jetted?

It needs to be jetted a lil higher, but it seems to run decent w/o. Just pops a lil on deceleration.

So because it doesnt have that "lean condition" is this the reason it doesnt need to be jetted as high as other systems?

[400ex07]

Did any one who did this mod need to buy new flange nuts? I want to buy everything I need before I take off the head pipe.

[Ryan'07400ex]

Originally posted by 400ex07
Did any one who did this mod need to buy new flange nuts? I want to buy everything I need before I take off the head pipe.

x2

If u ask the honda dealer for " exhaust gasket for 400ex" will he know what ur talking about?

[rob_990]

yea mine did but they didnt have any in stock and i was fine without them.you might wanna buy new studs though if your taking your header off

[Bill Martin]

Originally posted by hornetgod13
I took a tip from TRXRacer1 and decided to open up the stock header. I took a few before and after pictures and measurements. The stock header collar welds are excessive and restrictive. With a little coaching and guidance from TRXRacer1, I used an assortment of dremel tool attachments to grind down and polish the welds to match the inside diameter of the header. The results were amazing! The before and after measurements showed an 11.2% (1/8") increase in each header pipes diameter. I'm not a rocket scientist but, I'm smart enough to know that an increase of airflow on a 4 stroke engine leads to more power.

This is an easy mod to do that took less than an hour to do from start to finish. It would go perfectly with a slip-on exhaust to maximize the benefit.

Here's some pictures...

Thanks I just ported my exhaust and was able to open it up quite a bit.
It was a pain in the @ss to swap the pipe out though, I have a over sized oil tank on it and it was tuff to get enough clearance but it's done.
I can't say how much it helped though I haven’t had a chance to get to the track yet.
It probably wont make much difference but any little bit helps.
Now as soon as I get the carb done that should help.

Thanks again for the tip!!!

[TRXRacer1]

Originally posted by rob_990
yea mine did but they didnt have any in stock and i was fine without them.you might wanna buy new studs though if your taking your header off No need for new studs.

[dankbud42o]

just did this over the weekend, took me forever to grind that down with a dremel lol. thanks for the tip :)

[rob_990]

Originally posted by TRXRacer1
No need for new studs.

there most likely gonna be bent and rusted and there less than a dollar a piece

[TRXRacer1]

Originally posted by rob_990
there most likely gonna be bent and rusted and there less than a dollar a piece Bent and rusted. :ermm:

I doubt bent to a point of replacement and what do you do after your first ride when they rust again? It's unnecessary work period.

[rob_990]

my headers are a b**** to get off.the thing that the studs hold are slightly warped and almost everytime they come out bent

[TRXRacer1]

That's fair. I think it's safe to say most people may struggle a little but it's not horrible. The problem is the hold down plates get bent. The studs will get tweaked again when you torque down so it's pointless to replace. Just tap the plates back on the studs and button it up (the job).

[tri5ron]

Can we vote for this thread to be added to the sticky list,"most popular 400ex threads"?

If so, then I nominate this thread to be added.

I realize that this is not a democracy,
(actually that is a good thing here),
and Pap's has the final say....
(that's ALSO a good thing here)

So What say, Pappy???

[TRXRacer1]

Originally posted by tri5ron
Can we vote for this thread to be added to the sticky list,"most popular 400ex threads"?

If so, then I nominate this thread to be added.

I realize that this is not a democracy,
(actually that is a good thing here),
and Pap's has the final say....
(that's ALSO a good thing here)

So What say, Pappy??? It is a highly popular mod and it has been written up very well here.

[honda01400ex]

hey im looking at doing the same thing could you tell me what you used to grind the welds out?

and were i can get them?

and hoe much do they cost?

thx

[honda01400ex]

hey im looking at doing the same thing could you tell me what you used to grind the welds out?

and were i can get them?

and hoe much do they cost?

thx

[Ryan'07400ex]

Originally posted by honda01400ex
hey im looking at doing the same thing could you tell me what you used to grind the welds out?

and were i can get them?

and hoe much do they cost?

thx

I used a dremel tool and a vice to hold it and then off course you have to have the tools to get the header off of the bike.

the first page also says what the guy used which I think was a dremel with different sizes I just used one size the whole time.

[honda01400ex]

hey im looking at doing the same thing could you tell me what you used to grind the welds out?

and were i can get them?

and hoe much do they cost?

thx

[Ryan'07400ex]

Originally posted by honda01400ex
hey im looking at doing the same thing could you tell me what you used to grind the welds out?

and were i can get them?

and hoe much do they cost?

thx

I just answered you above and if that aint good enough why don't you try searching yourself instead of depending on us to find your crap. You've ask three times already. geez... try finding it yourself. IT isn't hard to search dremel tool, i just did it

DO IT BEST - Downs Lumber & Bldg. Materials

ACE HDWE & APPLIANCES

WAL-MART

FASTENAL

LOWE'S

Price for one at walmart was 53 dollars idk if its good enough for you or not.
Just search those places

[TRXRacer1]

Originally posted by Ryan'07400ex
I just answered you above and if that aint good enough why don't you try searching yourself instead of depending on us to find your crap. You've ask three times already. geez...

Yeah I gotta agree, that 3 time **** was getting stupid.

[dalejiw25]

Beatin a dead horse here peeps. close this thread already. tired of seeing it.

[dubee]

So is there still no one who can tell how much this works??

[Ryan'07400ex]

Originally posted by dubee
So is there still no one who can tell how much this works??

I didn't do this by itself but it's free (if you have access to a dremel tool) so might as well try.

[wolf400]

yea does it really help that much? im doing mine right now i was just wonden if anyone could feel power diff or anything?

[H400DAN2004]

Originally posted by wolf400
yea does it really help that much? im doing mine right now i was just wonden if anyone could feel power diff or anything?

i guess your the pig to let us know. im also about to do this but im waiting on a few things also to put on so i wont be a good person to reply the differences

[mycat8urskidoo]

A carbide burr bit on a die grinder will have that thing cleaned up in less than 5 minutes a side, I couldnt imagine that much grinding with a dremel